<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    #d1{
      width: 400px;
      height: 200px;
      border: 20px solid red;
      /*设置圆角,值越大越圆, 超过宽高一半为正圆(前提是正方形)*/
      border-radius: 200px;
    }
    #d2{
        width: 50px;
        height: 50px;
        border:1px solid red;
        /*给元素添加内边距会影响元素的显示宽高*/
        padding-left: 50px;
        padding-top: 50px;
    }
  </style>
</head>
<body>
<ul>
    <li>aaa</li>
    <li>bbb</li>
    <li>ccc</li>
</ul>
<div id="d2">内边距</div>
<!--div#d1   +tab    div.c1   +tab-->
<div id="d1">边框测试</div>
</body>
</html>